Accelerated cooling process for reactors

ABSTRACT

A process for shutting down a hydroprocessing reactor and for removing catalyst from the reactor, wherein the reactor includes a quench gas distribution system. The process comprises shutting off hydrocarbon feed to the reactor, stripping hydrocarbons from the catalyst, and cooling the reactor to a first threshold reactor temperature in the range of from 375-425° F. (190-218° C.). At least a portion of circulating gaseous medium flowing to the reactor is then routed through a temporary heat exchanger and cooling the gas to not less than 40° F. (4° C.). Once cooled, mixing the cooled gas with the circulating gaseous medium flowing to the reactor. Continuing steps routing and cooling until a second threshold temperature is reached wherein the reactor temperature is in a range between 120° F. and 250° F. (49° C.-121° C.). The reactor can then be purged with N 2  gas, followed by introducing water into the reactor via the quench gas distribution system. The catalyst can then be safely removed from the reactor.

TECHNICAL FILED

This disclosure relates to accelerated processes for shutting down ahydroprocessing reactor and for removing catalyst from the reactor via awater flooding technique.

BACKGROUND

Hydroprocessing units are fixed bed catalyst systems that must bechanged periodically when the catalyst is spent. Other maintenance canalso be conducted at that time. It is important, however, that the unitshutdown procedures must be developed and executed with excellence toprotect personnel, prevent incidents, and to minimize costs andduration. Hydroprocessing reactor shutdown processes must be conductedwith maximum efficiency and minimum duration while safeguardingpersonnel and equipment.

To remove catalyst from the reactor, the catalyst and reactor shell mustbe cooled to less than 200° F. (93° C.) to enable water flooding of thereactor. One such process is described in U.S. Pat. No. 9,545,649, whichis incorporated herein in its entirety. As the reactor reaches about400° F. (204° C.), however, the cooling process slows down dramatically.There is a need to speed up the cooling below 400° F. (204° C.) andthereby allow faster catalyst changes for hydroprocessing units, whilealso safeguarding personnel and equipment.

SUMMARY

Provided is a process that once the catalyst temperatures during ahydroprocessing shutdown reach about 400° F. (204° C.), the use of atemporary heat exchanger installed in the recycle gas circulation systemis implemented. This has been found to solve the slow cooling issuebelow 400° F. (204° C.), while also safeguarding personnel andequipment.

In one embodiment there is provided a process for shutting down ahydroprocessing reactor and for removing catalyst from the reactor. Theprocess comprises shutting off the hydrocarbon feed to the reactor;stripping hydrocarbons from the catalyst; and cooling the reactor to afirst threshold reactor temperature in the range of from 375-425° F.(190-218° C.). Then, routing at least a portion of a gaseous mediumflowing to the reactor through a heat exchanger cooling the gas to notless than 40° F. (4.4° C.). Once cooled, mixing the cooled gas with gasmedium flowing to the reactor. Continue routing and cooling at least aportion of the gas medium flowing to the reactor, and then mixing thecooled gas with the flow to the rector, until the reactor temperature isin the range of between 120° F. (49° C.) and 250° F. (121° C.). In oneembodiment, the highest reactor temperature and/or the highest catalystbed temperature is in the range between 120° F. and 200° F. (49° C. and93° C.). The reactor is then purged with N₂ gas, followed by introducingwater into the reactor via a quench gas distribution system. Thecatalyst can then be safely removed from the reactor.

In another embodiment there is provided a process for shutting down ahydroprocessing reactor and for removing catalyst from the reactor. Theprocess comprises shutting off hydrocarbon feed to the reactor.Thereafter, hydrocarbons are stripped from the catalyst at a temperaturegreater than the final reactor operating temperature. After thehydrocarbon stripping step, cooling the reactor to a first thresholdreactor temperature in the range of rom 375-425° F. (190-218° C.). Afterthe first threshold temperature is reached, at least a portion of agaseous medium flowing to the reactor is routed through a temporary heatexchanger cooling the gas to not less than 40° F. Once cooled, mixingthe cooled gas with gas medium flowing to the reactor. The routing andcooling at least a portion of the gas medium flowing to the reactor, andthen mixing the cooled gas with the gas flow to the rector, iscontinued/repeated until the reactor temperature is in the range ofbetween 120° F. (49° C.) and 250° F. (121° C.). In one embodiment, thehighest reactor temperature and/or the highest catalyst beds temperatureis in the range between 120° F. and 200° F. (49° C. and 93° C.). Thereactor is then purged with N₂ gas, followed by introducing water intothe reactor via a quench gas distribution system. The catalyst can thenbe safely removed from the reactor.

In yet another embodiment there is provided a process for shutting downa hydroprocessing reactor and for removing catalyst from the reactor,with the process comprising shutting off hydrocarbon feed to the reactorand stripping hydrocarbons from the catalyst at a temperature above thefinal reactor operating temperature. The reactor is then cooled with H₂gas at a controlled reactor cooling rate to a first threshold reactortemperature in the range of from 375° F.-425° F. (190-218° C.). Thereactor also includes a quench gas distribution system, and at least aportion of the H₂ gas is introduced into the reactor via the quench gasdistribution system. At least a portion of a gaseous medium flowing tothe reactor is then routed through a temporary heat exchanger coolingthe gas to not less than 40° F. Once cooled, the cooled gas is mixedwith gas medium flowing to the reactor. The routing and cooling at leasta portion of the gas medium flowing to the reactor, and then mixing thecooled gas with the gas flow to the reactor is continued, until thereactor temperature is in the range of between 120° F. (49° C.) and 250°F. (121° C.). In one embodiment, the highest reactor temperature and/orthe highest catalyst beds temperature is in the range between 120° F.and 200° F. (49° C. and 93° C.). The reactor is then purged with N₂ gas,followed by introducing water into the reactor via the quench gasdistribution system. The catalyst can then be safely removed from thereactor. When the reactor is flooded with the water, dumping a catalystslurry from the reactor, wherein the dumped catalyst slurry comprisesthe catalyst and the water. Separating the water from the dumpedcatalyst slurry to provide separated water; optionally, recycling atleast a portion of the separated water to the reactor. After the dumpingstep, vacuuming residual catalyst from the reactor, thereafter,assessing the patency of a plurality of quench apertures of the quenchgas distribution system; and washing at least one internal component ofthe reactor with pressurized water. Furthermore, the controlled coolingrate is not more than (≤) 25° F. (14° C.) per 15 minute interval. Thewater introduced into the reactor during the water introducing step hasa temperature not less than (≥) 50° F. (10° C.) and a chloride contentnot more than (≤) 50 ppm.

Further embodiments of processes for shutting down a hydroprocessingreactor and for removing catalyst from the reactor are describedhereinbelow. As used herein, the terms “comprising” and “comprises” meanthe inclusion of named elements or steps that are identified followingthose terms, but not necessarily excluding other unnamed elements orsteps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents the typical flow of recycle gas througha hydroprocessing unit, with potential tie-in points for recycle gascooling indicated.

FIG. 2A is a schematic sectional view of a reactor having a quench gasdistribution system, according to an embodiment of the invention.

FIG. 2B shows a quench ring of the reactor of FIG. 2A as seen in planview.

DETAILED DESCRIPTION

Hydroprocessing reactor shutdown processes must be done safely toprotect personnel yet quickly to minimize lost production. Spentcatalyst has self-heating properties; in the presence of oxygen it canspontaneously heat up as it oxidizes. During conventional shutdowns,reactors have been kept under inert nitrogen during shutdown and cleanupto prevent catalyst contact with oxygen. Inert vessel entry, e.g.,entering a reactor under nitrogen gas, exposes personnel to possiblenitrogen asphyxiation and has resulted in fatalities. Also, onlyspecially trained personnel are allowed to enter reactors kept underinert conditions, thereby routinely preventing engineers from performinginspections, possibly leading to sub-standard work and premature futureshutdowns.

Shutdown processes as disclosed herein eliminate many of the problemsassociated with prior art shutdown procedures. Furthermore, shutdownprocesses as disclosed herein have the advantage of providing fast andefficient reactor cooling to a temperature allowing manual entry intothe reactor. The present shut down processes in fact accelerate thecooling process to thereby allow faster catalyst changes for thehydroprocessing units. With the faster catalyst change, the presentprocesses have the further advantage of minimizing damage to valuableequipment of a hydroprocessing system. Moreover, with the fastercatalyst change, the present processes have the additional advantage ofdecreased danger to personnel during reactor shutdown and cleaning. Suchshutdown processes may comprise a plurality of component methods, orphases, as described hereinbelow.

Shutting Off Hydrocarbon Feed to the Reactor

In an embodiment, processes for shutting down a hydroprocessing reactorand for removing catalyst from the reactor as disclosed herein(hereafter “shutdown processes”) may comprise shutting off hydrocarbonfeed to the reactor. Prior to shutting off the hydrocarbon feed, a finaloperating temperature of the reactor may be recorded.

Stripping Hydrocarbon from the Catalyst

After the hydrocarbon feed to the reactor has been discontinued,shutdown processes may further comprise stripping hydrocarbons from thecatalyst. Hydrocarbon stripping may be conducted at a temperaturegreater than the final reactor operating temperature. Prior to shuttingoff the hydrocarbon feed to the reactor, a final operating temperature,TF, of the reactor may be recorded. The reactor may then be heated abovetemperature TF to minimize the required stripping time.

In an embodiment, hydrocarbons may be stripped from the catalyst withcirculating H₂ gas at a minimum temperature not less than (TF+25° F.);that is to say, hydrocarbons may be stripped from the catalyst at atemperature at least 25° F. (14° C.) above the final reactor operatingtemperature. In an embodiment, hydrocarbon stripping may be conducted ata maximum temperature at, or approaching, the design limit of thereactor. In an embodiment, hydrocarbon stripping of the catalyst in thereactor may be continued for a minimum time period of 6 hours or notless than two hours after the latest time point at which liquidhydrocarbon is detected in the separators downstream of the reactor.

During the hydrocarbon stripping phase, recycled gas may be combinedwith makeup H₂. In an embodiment, reformer H₂ may be eliminated from thesource of makeup H₂ during the hydrocarbon stripping phase in order tominimize or prevent the introduction of liquefied petroleum gas (LPG)and benzene into the reactor. In addition, during the hydrocarbonstripping phase, all liquid hydrocarbons may be drained from low points,separators, and knock-out pots to prevent recontamination of thecatalyst with extraneous hydrocarbons.

Cooling the Reactor

The reactor may be cooled by circulating a gaseous medium through thereactor. In an embodiment, the gaseous medium may comprise a gasselected from H₂ gas, N₂ gas, and combinations thereof. In anembodiment, the gaseous medium circulating through the reactor maycomprise recycle gas together with makeup H₂, in which case reformer H₂may be removed from the makeup H₂ source during the reactor coolingphase to minimize catalyst contamination by benzene and lighthydrocarbons.

During the reactor cooling phase, the reactor temperature may bemonitored at a plurality of reactor locations, e.g., at a plurality oflocations on the reactor skin (exterior surface), while the reactor iscooled to a first threshold reactor temperature. The “first thresholdreactor temperature” is a reactor temperature in the range of from375-425° F. (190-218° C.), and in one embodiment about 400° F. (204°C.).

Unless otherwise specified, reference herein to “reactor temperature”refers to the highest temperature recorded at a given time point by aplurality of temperature indicators, wherein each temperature indicatoris configured for independently monitoring the temperature of thereactor skin at a corresponding plurality of reactor skin locations.

In an embodiment, the reactor cooling phase may comprise cooling thereactor at a controlled reactor cooling rate so as to prevent equipmentdamage. In an embodiment, the reactor may be cooled at the controlledreactor cooling rate to the first threshold reactor temperature withcirculating H₂ gas and/or N₂ gas. In an embodiment, reactor cooling tothe first threshold reactor temperature may be accelerated, within theconstraints of various cooling rate criteria for preventing equipmentdamage, e.g., by maximizing the gas circulation rate and by maximizingthe unit pressure.

Various criteria related to temperature differences, e.g., between thereactor inlet and outlet fluid temperatures and between differentlocations of the reactor, may be strictly adhered to during the entireshutdown process in order to minimize the risk of equipment damage.Changes in both flow rate and temperature of fluids introduced into thereactor should be made in steady increments to prevent abrupttemperature changes. In an embodiment, the rate of cooling the reactor,including the catalyst beds within the reactor, may be limited to notgreater than 25° F. (14° C.) per 15 minute interval.

The reactor may be cooled at a controlled cooling rate using one or moremethods for controlling the rate of reactor cooling. As non-limitingexamples, the rate of reactor cooling during the reactor cooling phasecan be controlled by adjusting various parameters, such as the gascirculation rate, the unit pressure, reactor effluent heat exchange withthe recycle gas, the furnace setting, and the recycle compressor speed(see, for example, FIG. 1, infra).

In an embodiment, the reactor may include a quench gas distributionsystem configured for distributing quench gas within the reactor duringreactor operation mode (hydroprocessing). During shutdown processes, thereactor cooling phase may comprise introducing at least a portion of theH₂ gas into the reactor via the quench gas distribution system. At thesame time, a further portion of the H₂ gas may be introduced into thereactor via the reactor inlet (see, for example, FIG. 2A). The use ofthe quench gas distribution system, in combination with the reactorinlet, for introducing the H₂ gas into the reactor may serve todistribute the H₂ gas within the reactor, resulting in more uniformcooling of the reactor and faster overall cooling of the reactor.

Accelerated Cooling

Once the shutdown proceeds as above and the reactor temperature reachesthe first threshold temperature in the range of about 375-425° F.(190-218° C.), e.g., about 400° F. (204° C.), a temporary heat exchangerwill be employed in the recycle gas circulation system of thehydroprocessing unit. The use of the heat exchanger is designed to solvethe slow cooling issue described above. A portion or all of the recyclegas from the recycle compressor will be routed through the temporaryheat exchanger and cooled to a minimum of 40° F. (4.4° C.) before mixingwith the recycle gas flowing to the reactor. Recycle gas may containvarious combinations of H₂, N₂, and other light hydrocarbon gases. Therecycle gas flowing through the heat exchanger will be cooled withpumped cooling liquid supplied by a temporary chiller. The coolingprocess will be complete when the hottest point of the reactor shellreaches a temperature between 120° F. and 250° F. (49° C. and 121° C.).In some units, the cooling may continue until the reactor temperatureand/or the catalyst beds reach a temperature between 120° F. and 200° F.(49° C. and 93° C.). The target temperature of the reactor shell and/orcatalyst will be selected based on specific unit requirements. Thistemperature is the second threshold temperature. Upon reaching thistarget temperature on the reactor shell or catalyst bed, the reactorwill then be placed under a N₂ atmosphere, and preferably blinded.

Nitrogen Purge

After cooling the reactor, the shutdown process may further compriseintroducing N₂ gas into the reactor to remove H₂ and light hydrocarbongases from the reactor. In an embodiment, H₂ and light hydrocarbon gasesmay be removed from the reactor by circulating N₂ gas through thereactor during at least one pressure/depressure cycle, e.g., byalternately pressuring and depressuring the reactor and associatedsystem (see, e.g., FIG. 1). In an embodiment, the N₂ gas introducingphase may involve a plurality of alternating pressure/depressure cycles,wherein the pressure in the reactor may be increased by the introductionof N₂ gas into the reactor to a relatively high pressure and thereafterthe reactor may be depressured by removing the N₂ gas from the reactorto provide a relatively low pressure in the reactor, and thepressure/depressure cycle may be repeated as appropriate.

At the termination of the purging phase, the shutdown process mayfurther comprise quantifying the hydrocarbon content of the effluentdischarged from the reactor; and, based on the hydrocarbon content,determining a lower explosive limit (LEL) for the reactor effluent.

After the hydrocarbons and H₂ gas have been removed from the reactor andthe catalyst contained therein is under inert conditions, the shutdownprocess may further comprise installing the blinds so as to isolate thereactor from liquid or gaseous hydrocarbon ingress. In an embodiment,the LEL for the reactor effluent will be determined to be less than 10%before the blinds are installed on the reactor. In an embodiment, thecatalyst may be maintained under inert conditions until the reactor hasundergone water flooding, i.e., for the duration of the waterintroducing phase of the shutdown process, infra.

During the N₂ gas introducing phase, the reactor may undergo furthercooling. Such cooling during the N₂ gas introducing phase may bepredominantly ambient cooling. The reactor may undergo still further(ambient) cooling during the installation of the reactor blinds.Generally, the cooling progresses to a temperature below 200° F. Thereis no need, however, to go below 120° F. since the next step is thewater introduction phase.

Introducing Water into the Reactor

After the N₂ purge, the water introducing phase of the shutdown processmay be commenced. The introduction of water into the reactor rapidlycools the reactor to a third threshold reactor temperature. The “thirdthreshold reactor temperature” may be defined herein as the reactortemperature at which personnel may safely enter the reactor. In anembodiment, the third threshold reactor temperature may be not greaterthan (≤) 120° F. (49° C.), or ≤110° F. (43° C.), or ≤100° F. (38° C.).

The water may be introduced into the reactor at a controlled reactorfill rate. In an embodiment, the maximum reactor fill rate may bedetermined for a given reactor according to the reactor dimensions,e.g., the diameter of the reactor. In an embodiment, e.g., when thereactor may lack a quench gas distribution system, the water introducingphase may be commenced at a relatively low reactor fill rate, e.g.,during a first fill phase, and the reactor fill rate may thereafter besequentially increased, e.g., during a second fill phase and a thirdfill phase of the water introducing phase. In embodiments wherein thereactor includes a quench gas distribution system, the water introducingphase may be commenced at a high (e.g., maximal) reactor fill rate viathe quench gas distribution system. In an embodiment, the reactor fillrate may be in the range from 25 to 400 gallons per minute (gpm) (about95 to 750 liters per minute), or from 35 to 350 gpm.

The water introduced into the reactor during the water introducing phasemay be at a temperature not less than (≥) 50° F. (10° C.). In anembodiment, the water introduced into the reactor during the waterintroducing phase may typically be at a temperature within the rangefrom 50° F. to 150° F. (10° C. to 66° C.), or from 50° F. to 100° F.(10° C. to 38° C.). In an embodiment, the water introduced into thereactor may be at ambient temperature and ambient pressure. The waterintroduced into the reactor during the water introducing phase may havea chloride content not greater than (≤) 50 ppm. In a sub-embodiment, thewater introduced into the reactor during the water introducing phase maybe selected from condensed water, industrial water, treated water,reverse osmosis water, and potable water, and combinations thereof.

In an embodiment, the water introducing phase may comprise flooding thereactor with the water. The term “flooding” may be used herein to referto introducing water into a hydroprocessing reactor to at leastpartially fill the reactor with water. During reactor flooding, at leastone catalyst bed of the reactor may be submerged by the water, andtypically all of the catalyst beds of the reactor may be submerged bythe water.

In an embodiment, preliminary to the water introducing phase, a maximumhydrostatic head pressure may be determined for a given reactor, whereinthe maximum pressure corresponds to a maximum amount of water in thereactor (e.g., when the reactor is completely filled). The increase inhydrostatic head pressure may be monitored during the water introducingphase. The water introducing phase may then be discontinued before themaximum hydrostatic head pressure is attained so as to avoid overfillingthe reactor. Applicant has observed that overfilling the reactor mayunnecessarily delay the shutdown process or startup, e.g., due tosaturated insulation slowing heatup of the reactor shell and subsequentreduced pressure operation. In an embodiment, the water introducingphase may be discontinued at a pressure 2-5 psi below (<) the determinedmaximum hydrostatic pressure for a given reactor.

In an embodiment, the reactor may include a quench gas distributionsystem, as is well known in the art of hydroprocessing. In anembodiment, the water introducing phase may comprise introducing atleast a portion of the water into the reactor via the quench gasdistribution system. The quench gas distribution system may comprise atleast one quench line and at least one quench ring in fluidcommunication with the quench line. Each quench ring may have aplurality of quench apertures, e.g., arranged at an upper part of thequench ring (see, e.g., FIGS. 2A-2B).

A water supply line may be coupled to at least one quench line fordistributing at least a portion of the water within the reactor duringthe water introducing phase. In an embodiment, most (>50%) of the waterintroduced into the reactor during the water introducing phase may beintroduced via the quench gas distribution system. In a sub-embodiment,all (100%) of the water introduced into the reactor during the waterintroducing phase may be introduced via the quench gas distributionsystem. Applicant has observed that introducing at least a portion ofthe water into the reactor via the quench gas distribution system servesto distribute the water more uniformly within the reactor, therebyavoiding localized cooling of the reactor so as to decrease the risk ofequipment damage.

In another embodiment, a substantial portion of the water introducedinto the reactor during the water introducing phase may be introducedvia the reactor inlet and/or via the reactor process outlet. Inembodiments wherein the reactor lacks a quench gas distribution system,all of the water introduced into the reactor during the waterintroducing phase may be introduced via the reactor inlet and/or thereactor process outlet.

Dumping Catalyst from the Reactor

When the reactor is at least partially filled with the water (e.g.,flooded), the shutdown process may further comprise dumping the catalystfrom the reactor. The reactor may comprise a plurality of catalyst beds.Typically, all of the catalyst beds will be submerged with the waterprior to commencing the dumping phase. In an embodiment, theintroduction of water into the reactor may be continued during thedumping phase, or, stated differently, the dumping phase may beconducted concurrently with the water introducing phase.

The catalyst dumped from the reactor may be in the form of a catalystslurry comprising the catalyst and the water. Water may be rapidly andefficiently separated from the dumped catalyst slurry using varioustechniques, including catalyst-water separation via mesh or screens ofdifferent configurations using, e.g., gravity or suction to remove thewater from the catalyst slurry (see, e.g., commonly assigned US PatentPub. No. 2014/0299558A1). The water separated from the dumped catalystslurry may be referred to herein as “separated water.” In an embodiment,the separated water may be recycled to the reactor. Recycling theseparated water to the reactor may serve to maintain hydrostatic headpressure, or to mitigate loss in such pressure, during the dumpingphase. In another embodiment, the separated water may be captured,stored, and/or treated, as described hereinbelow.

In an embodiment, the reactor may optionally be at least partiallyre-filled with water after an initial reactor dump, and the dumpingprocedure may be repeated. In an embodiment, during a procedure forre-filling the reactor with water after an initial dump, water may beintroduced into the reactor at the maximum fill rate for a givenreactor.

Vacuuming Residual Catalyst from the Reactor

In an embodiment, a portion of the catalyst may be retained within thereactor as “residual catalyst” after the catalyst dumping phase.Typically, the residual catalyst will represent only a small fraction ofthe total catalyst present in the reactor prior to commencement of thecatalyst dumping phase. In an embodiment, the shutdown process mayfurther comprise vacuuming any such residual catalyst from the reactorafter the dumping phase has removed most of the catalyst. By theexpression “vacuuming residual catalyst from the reactor” is meantremoving residual catalyst from the reactor via suction, e.g., using asuction device capable of drawing a partial vacuum. In an embodiment,the vacuuming phase may comprise vacuuming the residual catalyst withoutdisturbing the catalyst support balls, or the like, on the catalystsupport trays.

Removing residual catalyst from the reactor by vacuuming is faster thanprior art methods, such as shoveling or raking catalyst, therebyexpediting the shutdown process even further. Furthermore, personnelshoveling piles of catalyst are exposed to the risk of engulfment, whichcould result in injury or fatality; vacuuming residual catalyst from thereactor decreases or eliminates such risks. Removing residual catalystfrom the reactor by vacuuming has the added advantage of leaving lesscatalyst fines in the reactor internals, thereby decreasing the timerequired to wash the reactor internals (see, e.g., Washing ReactorInternals, infra). Reactor internals are disclosed, for example, incommonly assigned U.S. Pat. No. 8,202,498, Multiphase contact anddistribution apparatus for hydroprocessing.

Assessing the Integrity of Quench Systems

In an embodiment, the reactor may include a quench gas distributionsystem. The shutdown process may further comprise assessing theintegrity of the quench gas distribution system. In an embodiment,assessing the integrity of the quench gas distribution system may beconducted after the vacuuming phase for the removal of residual catalystfrom the reactor. The quench gas distribution system may comprise atleast one quench line, at least one quench ring in fluid communicationwith the quench line, and a plurality of quench apertures arranged at anupper part of each quench ring.

In a sub-embodiment, assessing the integrity of the quench gasdistribution system may include testing the system for leaks, e.g., atwelds and the flanges of each quench ring. In another sub-embodiment,assessing the integrity of the quench gas distribution system maycomprise assessing the patency of the quench ring(s) and of a pluralityof quench apertures of the quench ring(s). The expression “patency” asused herein with reference to the quench rings and quench aperturesrefers to the degree of openness of each such quench ring and aperture,or, stated differently, the lack of blockage of such quench ring(s) andapertures. In an embodiment, assessing the integrity of the quench gasdistribution system may involve coupling a water supply line to at leastone quench line for supplying water to the quench ring(s).

In an embodiment, a quench aperture having complete patency (i.e., noocclusion of the aperture) delivers water at a certain rate or in acharacteristic manner, e.g., to produce a water spout of a particularheight. In an embodiment, the degree of patency of each quench aperturemay be assessed, for example, based on the height of the water spoutdelivered therefrom. In an embodiment, the water supply line may becoupled to at least one quench line preliminary to filling the reactorwith water during the previously described water introducing phase, suchthat the same water supply line may be used to supply water to thequench rings for both the water introducing phase and the assessment ofquench system integrity.

Washing Reactor Internals

The reactor may include a plurality of internal components, e.g., forfluid mixing and distribution within the reactor during hydroprocessingoperations. Such internal components are generally known in the art, andmay be referred to collectively as reactor internals. The shutdownprocess may comprise washing at least one internal component of thereactor with pressurized water. In an embodiment, washing the reactorinternals may be done after assessing the patency of the quenchapertures, supra. Pressurized water can be used, even with pressuresranging up to 50,000 psi. However, in an embodiment, the reactorinternals may be washed using pressurized water at a pressure less than5000 psi. As a non-limiting example, the reactor internals may be washedwith water from a pressure washer capable of generating a maximumpressure <5,000 psi, e.g., using a domestic- or household grade pressurewasher. Advantageously, such pressure washers can be operated by allpersonnel. The use of pressure washers operating at a maximum pressure<5,000 psi speeds up the shutdown process and costs less, as comparedwith the use of higher pressure washers (operating at pressures >5,000psi) as used in some prior art processes.

Hydro-Drilling Aggregated Catalyst

During hydroprocessing operations, some of the catalyst may aggregate orform clusters of catalyst (e.g., due to coking). Occasionally, suchaggregated catalyst may remain in the reactor after the catalyst dumpingphase has terminated, and such aggregated catalyst may be difficult toremove from the reactor without the use of specialized equipment orprocedures.

In an embodiment, the reactor shutdown process may optionally include ahydro-drilling phase, wherein aggregated catalyst may be hydro-drilledin situ in the reactor. In an embodiment, the hydro-drilling equipmentfor removing aggregated catalyst during the hydro-drilling phase maycomprise a water-operated mechanical drill. In an embodiment, during thehydro-drilling phase, the hydro-drilling equipment may be disposedwithin the reactor for the in situ removal of the aggregated catalyst,while the hydro-drilling equipment may be operated remotely by personnellocated outside the reactor. Accordingly, the hydro-drilling techniqueeliminates the risk of personnel being engulfed in catalyst during theremoval of aggregated catalyst from the reactor. Hydro-drilling alsoavoids the use of mechanical work to break up the coked catalyst; suchmechanical work is slower and more labor intensive as well as being lesssafe.

Monitoring for the Presence of Nickel Carbonyl

In an embodiment, the catalyst may comprise dispersed nickel sulfides.Under certain conditions, carbon monoxide in the reactor may react withnickel sulfides to form nickel carbonyl (Ni(CO)4). Nickel carbonyl isknown to be highly toxic. Nickel carbonyl is also known to undergothermal decomposition at higher reactor temperatures, e.g., above 400°F. (about 200° C.), but may accumulate at lower temperatures during thereactor cooling phase.

Applicant has determined threshold carbon monoxide concentrations belowwhich the concentration of nickel carbonyl will be less than 1 ppb (theeight hour threshold limit value (TLV)). Accordingly, during the reactorcooling phase the shutdown process may further comprise recording thecarbon monoxide concentration of the effluent discharged from thereactor. In an embodiment, the reactor may not be cooled below a nickelcarbonyl threshold temperature (e.g., <400° F.) until carbon monoxide ispurged from the reactor and its associated system, e.g., the COconcentration of the reactor effluent has fallen below a carbon monoxidethreshold (e.g., 10 ppm). If the reactor temperature inadvertently fallsbelow the nickel carbonyl threshold temperature while the carbonmonoxide concentration remains above the carbon monoxide threshold, theshutdown process may further comprise re-heating the reactor above thenickel carbonyl threshold temperature for a time period sufficient tothermally decompose (i.e., eliminate) any nickel carbonyl that may haveformed.

Handling Waste Water from Reactor Flooding

As noted hereinabove, during or following the catalyst dumping phase ofthe shutdown process, water may be rapidly and efficiently separatedfrom the dumped catalyst slurry. In an embodiment, at least a portion ofthe separated water may be captured, analyzed for contaminants, andsubsequently treated in a waste water handling phase of the shutdownprocess. Separated water that is captured or stored for treatment mayalso be referred to herein as “waste water.”

In an embodiment, the waste water handling phase may comprisequantitatively analyzing the separated water for the presence ofcontaminants to provide quantitative contaminant data, and, based on thequantitative contaminant data, determining a schedule for releasing theseparated water to a refinery waste water system. During this phase ofthe shutdown process, the rate of releasing the waste water to therefinery waste water system may be carefully controlled to be within thetreating limits of the refinery waste water system.

Embodiments of the invention will now be further described withreference to the drawings. FIG. 1 schematically represents a system andscheme for the flow of a gaseous medium, e.g., comprising H₂ gas, duringshutdown of a hydroprocessing reactor.

For the sake of clarity, the description of FIG. 1 refers primarily toH₂ gas, it being understood that during various stages of the shutdownprocess a gaseous medium may comprise, for example, N₂ gas in lieu of,or in addition to, H₂ gas. The H₂ gas may also comprise minor amounts ofcomponents such as methane, ethane, propane, etc.

The system of FIG. 1 may comprise a first heat exchanger 110, a furnace120, a second heat exchanger 130, a separator 140, a recycle compressor150, and a reactor 200. In FIG. 1, each of first heat exchanger 110 andsecond heat exchanger 130 may comprise or represent one or a pluralityof heat exchanger units. Components of the system shown in FIG. 1 may beused during an operation mode (e.g., hydroprocessing) or a shutdownmode. The system in FIG. 1 also shows optional components, a feed pump160 and an H₂S absorber 170 downstream from the separator 140. Thesystem may be used in conjunction with various other components (notshown) during the operation mode as well as during the shutdown mode.Additional components (not shown) that may be used in conjunction withthe system may include, without limitation multiple separators, e.g.,hot and cold separators, additional heat exchangers, e.g., as preheatupstream or downstream from the feed pump, a distillation unit, and areactor effluent/distillation preheat exchanger.

During a shutdown mode of the system in FIG. 1, a shutdown process maycomprise a hydrocarbon stripping phase and a reactor cooling phase.During the hydrocarbon stripping phase, H₂ gas may flow from recyclecompressor 150 via lines 22 and 23 to first heat exchanger 110, via aline 24 to furnace 120, and via a line 28 to reactor 200. During thehydrocarbon stripping phase, first heat exchanger 110 and the furnace120 may be used for heating the recycle H₂ gas. The heated H₂ gas mayenter reactor 200 via the reactor inlet (see, e.g., FIG. 2A), and flowsthrough reactor 200 to strip hydrocarbons from the catalyst. The H₂ gasdischarged from the outlet of reactor 200 may be recycled via a line 34to second heat exchanger 130, and via separator 140 and lines 38 and 39to recycle compressor 150. Makeup H₂ gas may be delivered via a line 29for combination with the recycle gas from recycle compressor 150.

With further reference to FIG. 1, hydrogen flow during the cooling phaseof the shutdown process may differ from that in the hydrocarbonstripping phase. During the reactor cooling phase, H₂ gas may flow toreactor 200 via quench gas distribution lines 32 a, 32 b (see, e.g.,FIGS. 2A-2B) in addition to the reactor inlet. During the reactorcooling phase, first heat exchanger 110 may be used to control thereactor cooling rate by heating the recycle gas before it enters reactor200. Depending on the required rate of reactor cooling, at least aportion of the recycle gas may bypass first heat exchanger 110 via aline 26 to provide cooler recycle gas for increased reactor cooling.

Further cooling of the recycle gas may be provided by second heatexchanger 130. Furthermore, during the later stages of the reactorcooling phase, e.g., when the reactor temperature approaches thetemperature of the recycle gas from recycle compressor 150, thecompressor speed may be reduced to decrease the temperature of therecycle gas discharged from recycle compressor 150, thereby furtherincreasing the reactor cooling rate.

Recycle gas may be temporarily routed through a “temporary” heatexchanger from any point between the vapor outlet of the high pressureseparator to the reactor inlet. Alternately, the recycle gas may berouted from any point between the recycle compressor discharge and thereactor inlet. The temporary routing of the recycle gas may or may notinclude the quench gas flowing to the reactor. FIG. 1 shows the generalflow of recycle gas through a typical hydroprocessing unit. Somepotential temporary routings of recycle gas to the temporary heatexchanger are shown as an “x” in FIG. 1, but the present process is notlimited to the routings shown. Generally one temporary heat exchangercan be used to accelerate the cooling, but more than one can be used ifnecessary. The temporary routing of the recycle gas may include aportion or all of the recycle gas.

The coolant in the temporary exchanger may be any fluid mediumincluding, but not limited to cooling water, refrigerant, ambient air,nitrogen, hydrocarbon, etc.

The recycle gas circulation may occur at any pressure within thelimitations of all equipment (including temporary equipment) of thesystem. Pressure relief must be provided for the temporary equipmentconsistent with Industry Standards.

The temporary heat exchanger may be any type including, but not limitedto, shell-and-tube exchanger, hairpin exchanger, fin-fan exchanger, etc.

The temporary heat exchanger may be connected, but not limited to, oneof the following: hoses, piping, tubing, etc.

During the cooling process either with or without the temporary heatexchanger, the following limits for reactor cooling must be maintained:

1. System pressure must not exceed MPT pressure limits (typically ¼ ofreactor design pressure) unless ALL reactor skin points (includingnozzles) are above Minimum Pressurization Temperature (MPT);

2. Startup and shutdown fluids (gas or liquid) shall be 40° F. (5° C.)minimum;

3. Changes in flow rates and/or temperatures of fluids or gases used forreactor heat up or cool down should be made in steady increments. Limittemperature changes for skin and bed temperatures to 25° F. (14° C.) per15 minutes. These limitations do not apply during water flooding;

4. Cooling with recycle gas distributed between quench nozzles and thereactor inlet is preferred to cooling only through the inlet nozzle tominimize thermal stress and cooling time;

5. The inlet and outlet fluid temperatures must be within 300° F. (165°C.) of the skin temperatures on the corresponding nozzle and head orshell elevation while heating, and within 200° F. (110° C.) whencooling. Quench nozzle fluid temperatures are excluded from this limitbecause there is insulation between the fluid and the nozzle wall;

6. Each skin point must be within 400° F. (220° C.) of any adjacent bedtemperature point; and

7. The temperature difference between the fluid at the inlet and at theoutlet of the reactor shall not exceed 400° F. (220° C.).

With still further reference to FIG. 1, the shutdown process may alsoinclude a N₂ gas introducing phase. The N₂ gas introducing phase mayinvolve circulating N₂ gas through the reactor during at least onereactor pressure/depressure cycle. In an embodiment, during the N₂ gasintroducing phase N₂ gas may be injected, e.g., via a line 21, topressure reactor 200 and N₂ gas may be released, e.g., via a line 40, todepressure reactor 200. The N₂ gas introducing phase of the shutdownprocess is not limited to any particular scheme for N₂ gas flow.Injection of liquid N₂ is generally not allowed without the use of aspecial designed stainless steel injection nozzle. Use of liquid N₂ maycause brittle fracture in piping and equipment that is not specificallydesigned for this service. Injection of liquid N₂ directly into processequipment is not recommended.

In system/scheme of FIG. 1, reactor 200 may represent or comprise aplurality of reactors, which may be arranged in series or in parallel.Furthermore, some hydroprocessing units may have multiple modules thatcan be shutdown separately while other modules continue operating. It isto be understood that variations in the flow scheme of FIG. 1 may occurin some hydroprocessing units, e.g., the flow of H₂ gas or other gaseousmedium during reactor shutdown processes may be other than asspecifically shown in FIG. 1, without departing from the scope of theappended claims. The flow of H₂ gas during the hydrocarbon strippingphase and the reactor cooling phase of the shutdown process is notlimited to any particular scheme or hydroprocessing system.

As noted hereinabove, the shutdown process may also include a waterintroducing phase, during which reactor 200 may be flooded with water.The water introducing phase may involve introducing water, havingdefined chemical and physical parameters or characteristics, into thereactor at a controlled fill rate. The reactor may be water flooded andthe catalyst dumped as a slurry, or the catalyst may be dry dumped andthen the reactor water flooded. With water flooding of the reactor,there is no reason to cool the catalyst below 120° F. nor is there anyreason to cool the shell below 120° F. Water flooding the reactor allowscatalyst to be removed from the reactor in an air environment, avoidinghazardous inert entry procedures.

In an embodiment, water for flooding the reactor during the waterintroducing phase may flow to reactor 200 as schematically representedin FIG. 1.

With reference to FIG. 1, system/scheme may comprise reactor 200. Watermay be introduced into reactor 200 via a water supply line 42 coupled toquench lines 32 a, 32 b, wherein the water may be introduced intoreactor 200 in a distributed manner, e.g., via a plurality of quenchapertures (see, e.g., FIGS. 2A-2B). Alternatively or additionally, waterfor flooding reactor 200 may be introduced into reactor 200 at thereactor inlet via a line (not shown). In an embodiment, water forflooding reactor 200 may be introduced into reactor 200 via the reactorprocess outlet (the latter not shown).

When reactor 200 is flooded with water, the catalyst may be dumped fromreactor 200 via a line coupled to a catalyst dump pipe of reactor 200(see, e.g., FIG. 2A). The catalyst dumped from reactor 200 may be in theform of a catalyst slurry comprising the catalyst and the water. Thedumped catalyst (e.g., slurry) may flow to a water/catalyst separationunit for separating the water from the catalyst. In an embodiment, atleast a portion of the separated water may be recycled to reactor 200.Alternatively or additionally, at least a portion of the separated watermay flow to capture, storage, and/or treatment. The separated waterflowing to capture, storage and/or treatment may also be referred toherein as “waste water.” In an embodiment, the waste water may betreated by a refinery waste water system, e.g., as describedhereinabove. In an embodiment, reactor 200 may optionally be at leastpartially re-filled with water, e.g., via line 42, after an initialreactor dump, and the dumping procedure may be repeated.

FIG. 2A is a schematic sectional view of a reactor having a quench gasdistribution system. Reactor 200 may comprise a reactor inlet 201, areactor process outlet 203, and catalyst dump pipe 206. In anembodiment, reactor 200 may be substantially cylindrical and verticallyoriented. Reactor 200 may further comprise a reactor wall 220 and areactor exterior surface or skin 220′. Temperature indicators (notshown) may be disposed at a plurality of locations, e.g., on reactorskin 220′, for monitoring the reactor temperature during various phasesof the shutdown process.

With further reference to FIG. 2A, the quench gas distribution system ofreactor 200 may comprise first and second quench lines 32 a and 32 b influid communication with first and second quench rings 230 a and 230 b,respectively. First and second quench lines 32 a and 32 b may be influid communication with line 30 during the reactor cooling phase of theshutdown process for receiving H₂ gas from recycle compressor 150 (see,e.g., FIG. 1); and first and second quench lines 32 a and 32 b may be influid communication with line 42 during the water introducing phase ofthe shutdown process for receiving water. The direction of fluid flow(e.g., H₂ gas or liquid H₂O) through quench lines 32 a and 32 b isindicated by arrows in FIGS. 2A-2B.

FIG. 2A shows two quench rings 230 a and 230 b. In an embodiment,reactor 200 may have other numbers of quench rings, and the number ofquench rings may be equal to the number of catalyst beds of reactor 200.Shutdown processes as disclosed herein are not limited to reactorshaving any particular number(s) of catalyst beds or quench rings. Onlyone catalyst bed, 240 b, is shown in FIG. 2A for the sake of clarity ofillustration.

FIG. 2B shows quench ring 230 a of FIG. 2A as seen in plan view alongthe line 2B-2B of FIG. 2A. Quench ring 230 a may have a plurality ofquench apertures 232. Quench ring 230 a, including quench apertures 232,may be configured for the distribution of fluid (e.g., H₂ gas) flowingtherefrom. In an embodiment, quench apertures 232 may be arranged, atleast primarily, at an upper part of quench ring 230 a. Quench ring 230b may be essentially the same as, or substantially identical to, quenchring 230 a. Quench rings 230 a and 230 b may be assembled as a pluralityof sections using flanges (not shown), as is known in the art.

In reactors that lack a quench gas distribution system, gas(es) forcooling reactor 200 and liquid water for flooding reactor 200 may beintroduced into reactor 200 via reactor inlet 201. In an embodiment, thewater for flooding reactor 200 may be introduced into reactor 200 viareactor process outlet 203.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Furthermore, all ranges disclosed herein are inclusive ofthe endpoints and are independently combinable. Whenever a numericalrange with a lower limit and an upper limit are disclosed, any numberfalling within the range is also specifically disclosed.

Any term, abbreviation or shorthand not defined is understood to havethe ordinary meaning used by a person skilled in the art at the time theapplication is filed. The singular forms “a,” “an,” and “the,” includeplural references unless expressly and unequivocally limited to oneinstance.

All publications, patents, and patent applications cited in thisapplication are herein incorporated by reference in their entirety tothe same extent as if the disclosure of each individual publication,patent application, or patent was specifically and individuallyindicated to be incorporated by reference in its entirety.

The drawings are representational and may not be drawn to scale.Modifications of the exemplary embodiments disclosed above may beapparent to those skilled in the art in light of this disclosure.Accordingly, the invention is to be construed as including all structureand methods that fall within the scope of the appended claims. Unlessotherwise specified, the recitation of a genus of elements, materials orother components, from which an individual component or mixture ofcomponents can be selected is intended to include all possiblesub-generic combinations of the listed components and mixtures thereof.

That which is claimed is:
 1. A process for shutting down ahydroprocessing reactor and for removing catalyst from the reactor,wherein the reactor includes a quench gas distribution system, theprocess comprising: a) shutting off hydrocarbon feed to the reactor; b)stripping hydrocarbons from the catalyst; c) cooling the reactor to afirst threshold reactor temperature in the range of from 375-425° F.(190-218° C.); d) routing at least a portion of circulating gaseousmedium flowing to the reactor through at least one temporary heatexchanger and cooling the gas to not less than 40° F. (4° C.); e) mixingthe gas cooled in d) with the circulating gaseous medium flowing to thereactor; f) continuing steps d) and e) until a second thresholdtemperature is reached wherein the reactor temperature is in a rangebetween 120° F. and 250° F. (49° C.-121° C.); g) after step f), purgingthe reactor with N₂ gas; h) after step g), and when the reactor is atthe second threshold reactor temperature, introducing water into thereactor via the quench gas distribution system; and i) dumping acatalyst slurry from the reactor, the catalyst slurry comprising thecatalyst and the water.
 2. The process according to claim 1, wherein thefirst threshold reactor temperature is about 400° F. (209° C.).
 3. Theprocess according to claim 1, wherein the second threshold reactortemperature is not greater than 200° F. (93° C.).
 4. The processaccording to claim 1, wherein step b) comprises circulating H₂ gasthrough the reactor at a temperature at least 25° F. above a finaloperating temperature of the reactor.
 5. The process according to claim4, further comprising: j) at the termination of step g), quantifying thehydrocarbon content of the effluent discharged from the reactor; and k)based on the hydrocarbon content, determining a lower explosive limitfor the reactor effluent.
 6. The process according to claim 1, whereinstep c) comprises circulating H₂ gas through the reactor, and theprocess further comprises: l) during step c), recording the carbonmonoxide concentration of the effluent discharged from the reactor; andm) if the reactor temperature falls below a nickel carbonyl thresholdtemperature while the recorded carbon monoxide concentration is above acarbon monoxide threshold, re-heating the reactor above the nickelcarbonyl threshold temperature for a time period sufficient to thermallydecompose nickel carbonyl.
 7. The process according to claim 1, wherein:step c) comprises circulating H₂ gas through the reactor, the reactorincludes a quench gas distribution system, and during step c) at least aportion of the H₂ gas is introduced into the reactor via the quench gasdistribution system.
 8. The process according to claim 1, wherein: thewater introduced into the reactor according to step h) is at atemperature not less than 50° F., and the water introduced into thereactor according to step h) cools the reactor to a reactor temperaturenot greater than 120° F.
 9. The process according to claim 1, whereinstep h) comprises flooding the reactor with the water.
 10. The processaccording to claim 1, wherein the water introduced into the reactoraccording to step h) has a chloride content not greater than 50 ppm. 11.The process according to claim 1, further comprising: n) concurrentlywith step i), separating the water from the dumped catalyst slurry toprovide separated water, and o) recycling the separated water to thereactor.
 12. The process according to claim 1, wherein a portion of thecatalyst is retained within the reactor as residual catalyst after stepi), and the process further comprises: p) vacuuming the residualcatalyst from the reactor.
 13. The process according to claim 12,wherein the reactor includes at least one quench ring having a pluralityof quench apertures therein, and the process further comprises: q) afterstep p), supplying water to the quench ring; and r) during step q),assessing the patency of the quench apertures based on the height of awater spout delivered from each of the quench apertures.
 14. The processaccording to claim 1, further comprising: s) after step i), washing thereactor internals with pressurized water at a pressure less than 5,000psi.
 15. The process according to claim 1, wherein after step h) thereactor contains aggregated catalyst, and the process further comprises:t) after step i), hydro-drilling the aggregated catalyst.
 16. Theprocess according to claim 1, further comprising: u) after step i),separating the water from the catalyst slurry to provide separatedwater, v) quantitatively analyzing the separated water for the presenceof contaminants to provide quantitative contaminant data, and w) basedon the quantitative contaminant data, determining a schedule forreleasing the separated water to a refinery waste water system.
 17. Aprocess for shutting down a hydroprocessing reactor and for removingcatalyst from the reactor, the process comprising: a) shutting offhydrocarbon feed to the reactor; b) stripping hydrocarbons from thecatalyst at a temperature above the final reactor operating temperature;c) cooling the reactor with H₂ gas at a controlled reactor cooling rate,wherein the reactor includes a quench gas distribution system, andduring step c) at least a portion of the H₂ gas is introduced into thereactor via the quench gas distribution system and the reactor is cooledto a temperature in the range of from 375-425° F.; d) routing at least aportion of circulating gaseous medium flowing to the reactor through atleast one temporary heat exchanger and cooling the gas to not less than40° F. (4° C.); e) mixing the gas cooled in d) with the circulatinggaseous medium flowing to the reactor; f) continuing steps d) and e)until a second threshold temperature is reached wherein the reactortemperature is in a range between 120° F. and 250° F. (49° C.-121° C.);g) circulating N₂ gas through the reactor during at least onepressure/depressure cycle of the reactor; h) after step g), introducingwater into the reactor via the quench gas distribution system; i) whenthe reactor is flooded with the water, dumping a catalyst slurry fromthe reactor, wherein the dumped catalyst slurry comprises the catalystand the water; j) separating the water from the dumped catalyst slurryto provide separated water; k) optionally, recycling at least a portionof the separated water to the reactor; l) after step i), vacuumingresidual catalyst from the reactor; m) after step l), assessing thepatency of a plurality of quench apertures of the quench gasdistribution system; and n) washing at least one internal component ofthe reactor with pressurized water, wherein: the controlled cooling rateduring step c) is not more than 25° F. per 15 minute interval, and thewater introduced into the reactor during step h) has a temperature notless than 50° F. and a chloride content not more than 50 ppm.